1. Field of the Related Art
This invention relates to a torsion wrench for tightening or loosening a workpiece, more particularly to a torsion wrench which has an alarm assembly that can generate an alarm sound when a predetermined torsion force is applied on the workpiece.
2. Description of the Related Art
Generally speaking, when manipulating a torsion wrench to tighten or loosen a workpiece, an operator easily overtightens or fails to tighten sufficiently the workpiece because an improper torsion force is applied on the workpiece.
Accordingly, there is a conventional torsion wrench which can be adjusted so as to generate an alarm sound when a predetermined torsion force limit is reached in order to overcome the above-described drawback.
The conventional torsion wrench, as shown in FIG. 1, includes a tubular casing 1, a drive unit 2 and an alarm assembly. The drive unit 2 has a head portion (2a) that is adapted to engage a workpiece, and a shaft portion (2b) that extends into the casing 1 and that is mounted pivotally to an upper end of the casing 1.
The alarm assembly includes a knocker 3 disposed in the casing 1 and connected to a distal end of the shaft portion (2b). When the torsion force applied by the drive unit 2 on a workpiece reaches a predetermined limit, the knocker 3 separates from the distal end of the shaft portion (2b) to knock on the casing 1, thereby generating an alarm sound. A biasing member 4 is disposed in the casing 1 and has an upper end which abuts against the knocker 3 for biasing the knocker 3 toward the shaft portion (2b) to prevent separation of the knocker 3 from the shaft portion (2b) when the torsion force applied by the drive unit 2 has not yet reached the predetermined limit. An adjusting unit includes a rod 5 mounted movably in a lower end of the casing 1 and having an upper end that abuts against a lower end of the biasing member 4, and a sleeve member 6 sleeved rotatably on the casing 1 and connected to the rod 5. The rod 5 is movable along an axis of the casing 1 by virtue of rotation of the sleeve member 6 relative to the casing 1 in a known manner so as to adjust initial biasing force of the biasing member 4 to correspond with the predetermined limit.
However, when the conventional torsion wrench is manipulated to actuate a workpiece, the sleeve member 6 is easily rotated by accident. Thus, the rod 5 may be moved to change the initial biasing force of the biasing member 4. As a result, an untimely change in the predetermined limit set on the conventional torsion wrench may occur.
In order to overcome the above-described drawback, there is another conventional torsion wrench, as shown in FIG. 2, which further provides a lock unit 7 for locking the adjusting unit so as to maintain the predetermined limit.
The casing 8 of the conventional torsion wrench has several axially extending grooves (8a) formed in an outer peripheral wall thereof. The sleeve member 9 of the conventional torsion wrench has a notch (9a) formed in an outer peripheral wall thereof and a hole (9b) formed through the outer peripheral wall. It is noted that other parts of the conventional torsion wrench are substantially similar to those of the aforementioned conventional torsion wrench.
The lock unit 7 includes two positioning rings (7a, 7e), a steel ball (7b), a curved and elongated resilient piece (7c) (see FIG. 3), and a manipulating ring (7d).
Referring to FIG. 3, the steel ball (7b) is disposed in the hole (9b). The resilient piece (7c) has one leg that extends into the notch (9a) and another leg that abuts against the steel ball (7b). The manipulating ring (7d) is sleeved rotatably and non-slidably on the sleeve member 9 and has a circumferential recess (7d') formed in an inner wall thereof for receiving the resilient piece (7c) therein. The positioning rings (7a, 7e) (see FIG. 2) are mounted securely on sleeve member 9 to clamp the manipulating ring (7d) therebetween. The inner wall of the manipulating ring (7d) at the recess (7d') has four sections (a, b, c, d). The section (c) is closer to the sleeve member 9 than the sections (a, b, d).
Therefore, the manipulating ring (7d) can be rotated to a locking position, as shown in FIG. 4, in which the section (c) depresses the corresponding leg of the resilient piece (7c) toward the sleeve member 9 so as to push the steel ball (7b) into a corresponding one of the groove (8a) of casing 8, thereby connecting the sleeve member 9 to the casing 8. Thus, the sleeve member 9 cannot be rotated relative to the casing 8 to move a threaded rod (8b) (see FIG. 2) along the axis of the casing 8 to adjust initial biasing force of a biasing member as described hereinbefore. It is noted that the threaded rod (8b) is mounted threadably in a lower end of the casing 8 and has its distal end connected to the sleeve member 9 in a known manner. When the manipulating ring (7d) is rotated to an unlocking position, as shown in FIG. 3, the steel ball (7b) can be moved away from the corresponding groove (8a) so as to permit rotation of the sleeve member 9 relative to the casing 8 and then move correspondingly the threaded rod (8b). However, the conventional torsion wrench is complicated in construction and is quite inconvenient to operate.